The present invention relates generally to reciprocating knife cutters of the type used for cutting pattern pieces or other parts from single ply or low ply sheet materials, such as fabric. More particularly, the present invention relates to a high speed reciprocating knife cutter wherein the knife is driven by an eccentric drive mechanism and a cutting apparatus utilizing such a knife cutter. The invention also relates to a knife sharpener for a cutting apparatus.
A reciprocating knife cutter of a type well-known in the art is shown, for example, in U.S. Pat. No. 4,879,935. The cutter disclosed therein includes a reciprocating knife driven by an eccentric mechanism. The knife is made as a one-piece member having a lower cutting portion supported by guide means for reciprocation along a vertical guide axis, and,an upper, resiliently flexible drive portion connected to the drive mechanism. The drive portion flexes laterally in a plane perpendicular to the drive axis of the eccentric mechanism, which permits the knife to be reciprocated along the vertical guide axis. The disadvantage of such a cutter is that a long, flexible knife blade is required which, due to the forces imposed on the flexible drive portion of the blade, has a relatively short service life.
A second type of reciprocating knife cutter well-known in the art is shown in U.S. Pat. No. 2,869,231. The cutter disclosed in this patent also includes an eccentric drive mechanism which reciprocates a knife along a vertical axis. However, in this case the knife is rigid and is driven by a connecting rod which links the top of the knife to the eccentric drive. The inclusion of an extra connecting rod and its associated hardware between the drive and the knife results in a bulky, relatively heavy device which cannot be operated efficiently at high speed. Moreover, the large number of moving parts present in such a device require constant maintenance.
A further disadvantage in many applications associated with both types of cutters described above is that reciprocation of the knife along a strictly vertical axis causes the knife to cut in both its downward and upward strokes as it passes though the sheet material. Cutting during the upward stroke of the knife tends to lift the sheet material from the horizontal surface on which it is supported in a spread condition during the cutting operation. Typically, the sheet material is held down against the support surface by vacuum applied from below. The tendency of the knife to lift the sheet material on the upstroke requires that more vacuum be applied to the material than would otherwise be required in order to insure that the material remains flat against the support surface during the cutting operation.
Cutting apparatus of the type discussed above, as well as butting apparatus in general, typically have an associated knife sharpener supported directly by the knife cutter. While such an arrangement places the sharpener in close proximity to the cutting blade for periodic sharpening between cutting operations, the sharpener adds weight to the knife cutter making it more difficult to overcome the inertial forces which tend to hinder rapid and precise movement of the cutter with respect to the sheet material being cut.
It is, therefore, an object of the invention to provide a high speed reciprocating knife cutter driven by an eccentric mechanism which does hot require either a resiliently flexible knife, or a connecting rod between the knife and the eccentric mechanism.
It is a further object of the invention to provide such a knife cutter which does not tend to lift the sheet material from the support surface during the upstroke of the knife.
It is a still further object of the invention to provide a knife cutter which provides for the use of an easily manipulated, low cost knife.
It is a yet another object of the invention to provide a knife sharpener for a cutting apparatus.
The present invention meets these and other objects by providing, in one aspect, a novel reciprocating knife cutter rich includes a frame, an eccentric drive member supported on the frame for rotation about a horizontal eccentric drive axis fixed relative to the frame, and an elongated knife having an upper part and a lower part which together define a longitudinal knife axis. The upper part of the knife is connected to the eccentric drive member for rotation therewith about the eccentric drive axis. The lower part of the knife has a sharpened cutting edge extending along at least a portion of its length, and means are provided for supporting the lower part of the knife for oscillation in a plane perpendicular to the eccentric drive axis. Means are also provided for slidably mounting the knife on the support means so that as the upper part of the knife is rotated and the knife reciprocates, the lower part of the knife oscillates and the knife and the support means slide relative to one another along the knife""s longitudinal axis.
Since the knife is not reciprocated along a strictly vertical axis, but is instead reciprocated in a plane perpendicular to the drive axis, the cutting edge of the knife is caused to follow an arcuate trajectory. Accordingly, as the cutter is moved along a cutting path on sheet material supported in a spread condition beneath the cutter, the cutting edge of, the knife moves forward or reward with respect to the cutting path during the knife""s downward stroke, depending on the direction in which the eccentric drive member rotates. Since the cutting action of the knife is increased when the cutting edge is moving forward with respect to the cutting path, the knife can selectively be made to cut more effectively on either its upward or downward stroke by controlling the direction in which the eccentric drive member rotates.
This provides a number of important advantages. By rotating the drive member so that the knife cuts primarily on its downward stroke, the problem of the knife lifting the sheet material from the support surface on its upward stroke can be substantially reduced. Accordingly, significantly less vacuum is required to hold the sheet material in place against the support surface during the cutting operation than is required with prior art cutters wherein the knife is reciprocated along an attack angle fixed perpendicularly to the cutting path. In many cutting operations where only one or two plys of a relatively heavy sheet material are being cut, no vacuum need be applied to the material to insure that i remains flat against the support surface.
Any deficiency in cutting speed lost by reducing or, eliminating cutting action on the upstroke of the knife is more than offset by the very high speed with which the present reciprocating knife cutter can be operated. Due to its simple construction which eliminates the need for either a flexible knife blade or a connecting rod between the eccentric drive and the knife, the reciprocating cutter of the present invention can operate at speeds of 20,000 rpm or more, which far exceeds the operating speeds of prior art reciprocating cutters. Moreover, cutting efficiency is increased because, as pointed out above, in this particular mode of operation the present cutter does not tend to lift the sheet material from the support surface during the upstroke of the knife.
Contrary to the above-described mode of operation, and as those skilled in the art recognize, there are certain cutting operations and/or types of sheet materials here it is desirable to have the knife cut primarily on its upward stroke. To meet the requirements of such situations, the rotation of the eccentric drive is simply reversed from the direction describe above so that the cutting edge of the knife moves forward with respect to the cutting path during the knife""s upward stroke and reward with respect to the cutting Path as the knife moves through its downward stroke.
Preferably, the support means pivotally supports the lower part of the knife for oscillation about a pivot axis disposed parallel to the eccentric drive axis and fixed relative to the frame at a position vertically below the drive axis. Thus, as the upper part of the knife is rotated and the knife reciprocates, the lower part of the knife oscillates about the pivot axis in a plane perpendicular to the eccentric drive axis, and the knife and the support means slide relative to one another along the knife""s longitudinal axis.
Regardless of the particular means utilized for supporting the lower part of the knife, it is preferable that the support means be movable with respect to the frame. By changing the position of the support means on the frame, the arcuate trajectory followed by the cutting edge of the knife can be adjusted so that the forward or rearward movement of the cutting edge with respect to the cutting path can be selectively increased or diminished over the degree of movement presented when the support means is located vertically below the eccentric drive axis.
In the-most preferred embodiment of the invention, the means for pivotally supporting the lower part of the knife includes a blade guide carried by the frame for oscillation about the pivot axis. The guide slidably engages the bottom part of the knife, and the two are thereby constrained to slide relative to one another along the knife""s longitudinal axis and oscillate together about the guide axis in a plane perpendicular to the eccentric axis as the drive member rotates and reciprocates the knife.
According to a second aspect, the present invention provides an apparatus for cutting single or low ply sheet material. The apparatus includes a table having a penetrable support surface for supporting one or more layers of sheet material in a spread condition, the above-described cutter head for cutting the sheet material, a carriage for mounting the cutter head above the support surface for relative movement therewith in at least two coordinate directions, and means for moving the cutter head and the support surface relative to one another.
According to a third aspect of the invention, a cutting apparatus including a knife sharpener is provided. The apparatus includes a table having a support surface for supporting one or more layers of sheet material in a spread condition, a cutter head including a -knife, a carriage for mounting the cutter head above the support surface for relative movement therewith in at least two coordinate directions, and means for moving the cutter head and the support surface relative to one another. Means for sharpening the knife mounted on at least one of either the table or the carriage are also provided. The means for sharpening the knife includes, for example), a rotating disk or wheel, a driven endless belt, or a strip of abrasive material arranged along one side of the table adjacent the support surface.